This is hardly any news to anyone who cares, and those who should care the most are either not understanding what top-posting is in the first place or they’re not aware of that people like me think top-posting is an evil decease we need to extinguish.
My primary reason to hate top-posting is that it is fast and easy for the single user who writes the mail reply, but it gives more work to the large amounts of people who read it. When someone posts to a mailing list, one should rather expect that the single user would be the one to put in a little extra effort to make the result readable for the masses who will read it.
Top-posting also most often involves the habit of including the entire previous conversation in a quoted manner below.
A sensible post and quote ethic, is to only quote as much as you need from the previous conversation to make your point clear, and to respond in a way so that it is clear to what parts of the quotes you are referring to. That more or less implies doing “interlaced” or “inlined” posting, where you show a few lines of quotes and then a few lines of comments over and over until the end of the mail.
The act of doing bottom-posting but keeping the entire thing quoted above the new text you add is almost as bad as top-posting. You remove the focus of what you write by providing far too much irrelevant text. Remove the irrelevant parts!
These days large portions of the modern world use broadband connections so the actual size of the mail is not a concern for bandwidth or speed reasons, but you probably still want the receivers to focus on your actual point. Also, a lot of mails these days end up in web archives or similar so they are then searchable by internet search engines and browsable by future people and then you even more want the mail to be on topic to become more relevant and less misleading to searches.
In case it isn’t obvious: this of course primarily concerns mails sent to (largish) mailing lists.